STRUCTURE-REACTIVITY CORRELATIONS FOR THE FORMATION OF ZIRCONOCENE ETA-2-IMINE COMPLEXES FROM AMINES

The formation of eta2-imine-zirconocene complexes (zirconaziridines) ( CP2Zr(NR1CR2R3) by elimination of R4H from CP2Zr(R4)(NR1CHR2R3) has be en investigated with regard to the variation in R1, R2, R3, and R4, in particular by making use of Hammett type structure/rate correlations (R1, R2, R4 = p-XC6H4, X = Me2N, MeO, H, Cl, CO2Me; R1, rho = 3.2; R2, rho = 0.5; R4, rho = -1.6). The elimination is first order in the zir conocene complex, has a deuterium isotope effect for the hydrogen elim inated of 8.2 at 20-degrees-C, and kinetic studies on Cp2Zr(Me)(NPhCHM e2) give the activation parameters DELTAH(double dagger) = 100 kJ mol- 1 and DELTAS(double dagger) = -19 J K-1 mol-1 for the elimination of m ethane. A cyclometalation involving deprotonation alpha to nitrogen by (R4)- best fits the data. The relationship between the rate of the re action and the structure of the amine shows a marked dependency on bot h electronic and steric effects ranging between no reaction after 48 h at 110-degrees-C for piperidine to below room temperature for silylam ines and benzylanilines. For the first time.eta2-imine complexes have been formed even from simple amines such as dibutylamine and trapped w ith an alkyne to form secondary allylic amines on workup. In the absen ce of a trap eta2-(PhN=CMe2)ZrCP2 rearranges via a rapidly reversible hydride shift to afford a eta3-azaallyl-zirconocene hydride.